More Proof of the Effects of Global Warming? Past 10 Years Were Hotter Than Previous 1,300 in Northern Hemisphere

When I wrote last week about how at least one scientist believes we are witnessing the "death spiral" of Arctic sea ice, even though this year's summer melt-off may not surpass the record set in 2007, a number of commenters seized upon that to jump to the conclusion that perhaps things aren't so bad as we thought. It even brought out of a couple of genuine climate change deniers. Just in case anyone was wondering, the trend in the Northern Hemisphere is solidly towards more warming:

According to a new study by researchers at Penn States' Earth System Science Center, and published in the online edition of the Proceedings of the National Academy of Sciences, "surface temperatures in the Northern Hemisphere were warmer over the last 10 years than any time during the last 1300 years" (ENS).

New Data Analyzed, Older Conclusion ConfirmedThis new finding was made using proxies for tree-rings (marine and lake sediment cores, ices cores, coral cores) and confirms earlier studies about long term warming trends.

Michael Mann, director of the Earth System Science Center,

Ten years ago, we could not simply eliminate all the tree-ring data from our network because we did not have enough other proxy climate records to piece together a reliable global record. With the considerably expanded network of data now available, we can indeed obtain a reliable long-term record without using tree rings.

Include Tree Rings and the Trend Extends Back to 300 CEThe issue with tree rings is that older trees put on narrower rings than younger trees and when comparing the two it is possible that some information about long-term climate trends can be lost. If tree-ring data is included, the same warming trend conclusion holds true going back 1700 years.

Mann was quoted by the BBC as saying that this means the now-familiar hockey stick chart, made famous in An Inconvenient Truth, is "alive and well".

Researchers note that "Conclusions are less definite for the Southern Hemisphere and globe" due to sparser proxy data available in the Southern Hemisphere.